qemu.test: Update the cd format in win_virtio_update

Update the cd_format to use ide or ahci, otherwise it may cause
problem during the block device driver install process.

Signed-off-by: Yiqiao Pu <ypu@redhat.com>
Merge pull request #123 from ypu/win_virtio_update

qemu.test: Update the cd format in win_virtio_update